Electric cable



March 30, 1943.. Y l H, L SEEDE v 2,315,039

' ELEcTnIc CABLE Filed oet. 3, 1941 g INVENTLOR l BY ff/4%, mMMwM/f' ATTORNEYSA ?atented Mar.v 30, 1943 2,315,039 ELECTRIC CABLE Harry L. Beede, Fort Lee, N. J., assignor to The- Okonite-Callender Cable Company, Incorporated, Paterson, N. J., a corporation of New Jersey Application October 3, 1941, Serial No. 413,445

(CLIM- 14) 4 Claims.

My invention relates to an improvement in electric cables and particularly to electric cables in which the cable conductor is Iwrapped with paper tape or other suitable insulating material which in the finished cable is impregnated with an insulating fluid such as oil. It is usual in such constructions to enclose the cable in a close fitting lead sheath.

it is a well recognized fact in the industry that despite the care exercised in insulating such cables and in purifying the impregnating oil to remove any impurities that may be present some of the desirable characteristics of the cable decrease with use owing to deterioration of the oil. This deterioration is in a large measure accelerated by the catalytic action of the metal conductor and the metal sheath on the dielectric immediately adjacent the Vconductor and sheath, the products thus formed moving into the cable dielectric in the operation of the cable. k

c It becomes an object of my invention to prevent the movement of these impurities into `the main body of the cable insulation by employing a filter barrier immediately adjacent the conductor and immediately adjacent the sheath, the

filter barrier being surrounded by electrostatic shielding. v

Prior to my invention it has been suggested that a filter medium such as carbon black be incorporated in the cable.` However, this filter medium in these prior structures has always been a part of the dielectric and hence under electrical stress.-

This is undesirable and becomes more so as the filter medium becomes saturated with oil decomposition products.

I am aware also that in other oil impregnated cables metal tapes have been employed immediately about the cable conductor for the purpose of providing a smooth surface at the conductor periphery in an attempt to eliminate the concentration of electric stresses at the conductor surface. Such metal tapes of course have no function as a filter medium.

sheath of the cable, the inner face of this tape being metal coated to provide an electrostatic shield.

This then provides a construction wherein the main body of the cable insulation is intermediate two electrostatic shielding layers or surfaces; a filtering medium lying intermediate this shielding and the cable conductor on the one hand and between the shielding and the cable sheath o the other hand.

In addition to the advantages accruing to a construction wherein a shielded filter medium is provided immediately adjacent the cable conductor and the cable sheath, my construction provides for increasing the length of the filterlng path in that the filtering path extends longitudinally of thecable instead of radially.

Regarding this extended filter path, let it be assumed, for example, that the cable is merely insulated with paper tape impregnated with a iilter medium as' suggested by the industry prior to my invention. It is quite evident that in such a cable the fluid dielectric, oil, is free to move radially of the cable'through the paper layers. With my improved construction, however, the path which this fluid dielectric must take is many times increased due to the fact that one face of the filter medium is metallized which provides a barrier against radial movement of the fluid dielectric. As a consequence, therefore, the fluid dielectric must move longitudinally from one barrier layer to another until it has reached that part of the insulation which is no longer metallized.

It is to be understood that the metal employed for metallizing the paper is one which does not react to a detrimental extent with the oil of the cable. It is well known that metals differ widely so far as their reaction with oil is concerned. The

metal which I prefer is aluminum inasmuch as vthis metal does not react with insulating oil.

Referring to Figs. 1 and l2: This embodiment of my invention comprises a conductor 2 which is of usual construction. Wrapped about this conductor are one or more layers of filter wrappings designated 4. f

The material employed for the filter wrappings may be paper tape impregnated with filtering material such as carbon black or other iilter aids. On the other hand, the lter mappings may not be impregnated at all but-may be a filter paper, many suitable types of which are available in the open market. 'One face of the filter wrapping or tape is metallized as shown at 5.

As above mentioned, the metal selected should be one which does not react to a detrimental extent with the uid insulating medium withV which the cable is finally impregnated. Aluminum is an example of such a metal.

In applying the filtering tape the same is wrapped about the conductor with the metallized surface of the tape facing outwardly to provide an electrostatic shield about the tape.

I prefer that the filter tape be wound with an overlap and if more than one layer is applied then the wraps of one layer break joints with the next succeeding layer.

VOver thisiilter barrier I apply the usual insul lating papertape designated 8.

Over the insulating paper tape 8 I apply one or more layers of metallized filter material I0 similar' to the lte'r'tape already referred to. I

prefer that this filter tape I0 beintercalated with metal tape, similar to the usual electrostatic shielding tape employed in lead sheathed cable. It is to be understood that the filter tape i0 is so applied that its inner face is the one which is metal coated. It will be appreciated, therefore, that with respect to the outer 1lter it is so applied that the filter is electrostatically shielded from the main body of the cable insulation.

On the exterior of the cable is the usual lead sheath Il. 'Ihe cable, it is to be understood, will be impregnated with insulating oil prior to the Iapplication of the sheath in accordance with usual cable practice.

It will be quite apparent from all of the foregoing that any decomposition products that are formed in the oil or other insulating fluid employed in tche cable as, for example, by reason of the reaction between the insulating uid and the cable conductor or the cable sheath, will be filtered out and hence their movement into the main body of the cable insulation prevented, this action being asma-ed by reason of the fact that the presence of the metallized face on the lter tape tremendously increases the iilter path of the fluid insulation.

It will be apparent, furthermore, that by reason of the provision of the metallic backing or face on the lter tapev and by reason of the fact that this metallic surface faces away from the conductor at the center of the cable and away from the sheath at the periphery of the cable, the filter layer itself both at the conductor and at the sheath is shielded, this shielding always being interposed between theL filter medium and the main body of the cable insulation.. 'I'his is of material advantage particularly when the filter becomes saturated with any decomposition prod# ucts formed as the result of operation of the cable.

In the embodiment of the invention as illustrated in Fig. 3 I show the invention applied to a three conductor cable. Each conductor of this cable is insulated as described in connection with Fig. 1. The usual fillers are designated I6. About the assembly of insulated conductors and fillers I apply metal binding tape I8, the metal sheath I4 being applied about the entire structure. This cable, it will be understood, possesses all of the advantageous features present in the construction of Fig. 1.

sulating material with the metal layer facing It is to be understood that changes may be made in the details of construction above described without departing fromv the spirit and scope of the invention.

What I claim is:

l. An electric cable impregnated with an insulating fluid, said cable comprising in combination a conductor which is of such nature as to contaminate insulating uld contacting the same, a composite tape, comprising a layer of filtering medium and a continuous layer o! metal which is inert with respect to the said insulating iiuid, wrapped helically about the conductor with the metal layer facing outwardly ofv the cable, insulating material, which is pervious to and impregnated with the insulating fluid, applied about the said composite tape, and an enclosing outer metal sheath, whereby in order that the insulating fluid of the cable which has contacted the cable conductor may move into the said iiuid impregnated insulating material it must move lengthwise of the cable through the said filtering layer and about the edges of adjacent wraps of the said composite tape.

2. An electric cable impregnated with an insulating fluid, said cable comprising in combination a conductor. insulating material impregnated with insulating fluid applied about said conductor, a composite tape comprising a layer of filtering medium and a continuous layer of metal, which is inert with respect to said insulating uid, wrapped helically about said ininwardly oi' the cable, and an outer sheath of a metal of such nature as to contaminate the insulating fluid contacting the same, whereby in order that the insulating uid of the cable which has contacted the said sheath may move into the said uid impregnated insulating material it must move lengthwise of the cable through the said filtering layer and about the edges of adjacent wraps of the said composite tape.

-3. An electric cable impregnated with an insulating fluid, said cable comprising in com- 'bination a conductor which is of such nature as to contaminateinsulating fluid contacting the "same, a composite tape, comprising a layer of filtering medium and a continuous layer oi metal, which is inert with respect to the said insulating fluid, wrapped helically about the conductor with the metal layer facing'outwardly oi' the cable, insulating material which is pervious to and impregnated with the insulating fluid applied aboutsaid composite tape, a second composite tape, comprising a layer of filtering medium and a continuous layer of metal, which is ,inert Awith respect to said insulating fluid,

wrapped `helically about said insulating material with the metal layer facing inwardly of the cable, and an enclosing outer sheath of Aa metal of such nature as to contaminate the insulating fluid contacting the same, whereby in order that the insulating fluid of the cable which has con- 4. An electric cable impregnated with insulating fluid, said cable comprising in combination a conductor which is of such nature as to contaminate insulating iluid contacting thefsame, a. composite tape, comprising a layer of filtering medium and a continuous layer of metal which is inert with respect tothe said insulating iiuid,`

wrapped heically about the conductor with the metal layer facing outwardly of the cable, insuiating material pervious to and impregnated with the insulating uid applied about the safid composite tape, a compositetape comprising a layer of filtering medium and a continuous layer of metal which is inert with respect to the said insulating fluid'and intercalate'd with a metal tape wrapped about the said insulating material with the metal layer facing inwardly of the cable, and an enclosing sheath ofl metal of a nature to contaminate insulating iiuid contacting therewith, whereby a shield is provided intermediate the filter medium at the center and at the periphery of the cable and the said pervlous insulating material of the cable, and whereby in order that the insulating uid o1' the cable which has contactedv the cable conductor and the cable sheath may move into the said fluid impregnated insulating material it must move lengthwise of the cable through the 10 mentioned ltering layers and about the edges of adjacent wraps of the said composite tapes.

HARRY L. BEEDE. 

